A method for obtaining reaction kinetic parameters using online reaction calorimetry

Abstract

The present invention discloses a method for obtaining reaction kinetic parameters by using online reaction calorimetry technology. The present invention uses online reaction calorimetry technology to obtain a real-time heat release rate curve at a certain reaction temperature by designing an experiment, and then obtains a real-time heat conversion rate curve. Finally, simple calculation and fitting can be performed to obtain the reaction order and rate constant; then, the rate constant at the corresponding temperature is obtained by experiments at different reaction temperatures, and activation energy and pre-exponential factor can be obtained by simple calculation and fitting. The method is simple and convenient, does not require the use of professional chemical software for complex calculations, and the obtained results are highly accurate.

Description

Technical Field

[0001] The invention relates to a method for obtaining reaction kinetic parameters, and in particular to a method for obtaining reaction kinetic parameters by using online reaction calorimetry technology. Background Art

[0002] Through the study of reaction kinetics, we can know how to control reaction conditions, increase the rate of the main reaction, inhibit or slow down the rate of the side reaction, so as to improve the output and quality of the product, reduce the consumption of raw materials, and reduce the burden of separation operations; we can also optimize the design and control for the industrialization of scientific research results and select the most suitable safe operating conditions for existing production. In the chemical industry, the selection of safe operating conditions is the first line of defense to prevent accidents caused by uncontrolled reactions.

[0003] Compared with reaction thermodynamics, reaction kinetics is much more complicated, so relatively speaking, reaction kinetics is still immature, and methods for obtaining reaction kinetic parameters are yet to be developed. Reaction kinetic parameters refer to the parameters contained in the rate equation. For the power function kinetic model, they usually refer to the reaction order, activation energy, and pre-exponential factor. The size of the reaction order indicates the degree of influence of concentration on the reaction rate. The larger the order, the greater the influence of concentration on the reaction rate. The higher the activation energy, the faster the reaction rate increases with increasing temperature, or the higher the activation energy, the more sensitive the reaction rate is to temperature. For a certain reaction, the higher the temperature, the greater the proportion of activated molecules, and the faster the reaction. If there are several reactions at the same time, high temperature is beneficial to reactions with high activation energy, and low temperature is beneficial to reactions with low activation energy. In production, this principle is often used to select a suitable temperature to accelerate the main reaction and inhibit side reactions.

[0004] At present, reaction kinetic parameters are mainly obtained by sampling at equal time intervals during the reaction process, using chromatography, spectroscopy, chemical analysis, etc. to obtain the trend of reactant concentration changes with reaction time, and finally calculating and fitting. The equal time interval sampling method cannot accurately obtain the process of rapid changes in reactant concentration, and may also miss important information about changes in intermediates.

[0005] Chinese invention patent CN112129890B discloses a method for accurately obtaining the kinetic parameters of the energetic material synthesis reaction process. This method uses a reaction calorimeter and a microcalorimeter to obtain a reaction process heat release rate curve, and then obtains a thermal conversion rate curve, and samples the reaction concentration at equal thermal conversion intervals, and finally uses the least square method in Matlab software to calculate and fit to obtain the reaction order and rate constant. Compared with the equal time interval sampling method, this method avoids the loss of important information in the equal time interval method, but because this method also requires the material to be taken out to measure the reactant concentration, for reactions with rapid changes in reactant concentration, the material is still continuing to react after being taken out, and there is still the problem of inaccurate reactant concentration detection, resulting in large differences between the obtained reaction kinetic parameters and the actual ones, and large errors. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a method for obtaining reaction kinetic parameters using online reaction calorimetry technology. The method does not require sampling, and parameters such as reaction exothermic rate and reaction exothermic enthalpy are directly obtained using a reaction calorimeter or obtained through simple calculation. Reaction kinetic parameters are calculated based on these parameters. The calculation results are accurate and reliable, overcoming the shortcomings of the current reaction kinetic parameters obtained by equal time interval sampling method and equal thermal conversion rate interval sampling method being different from the actual values ​​and having low accuracy.

[0007] The reaction kinetic parameters described in the present invention refer to the parameters included in the rate equation, and for a power function kinetic model, generally refer to the reaction order, activation energy and pre-exponential factor.

[0008] The present invention uses online reaction calorimetry technology to obtain reaction kinetic parameters, which refers to the use of a reaction calorimeter (such as RC1, Simular, etc.) to detect various required parameters in real time online. A reaction calorimeter is a tool used in chemistry and drug development to measure the heat absorption and release of physical and chemical reactions, usually including a stirred tank reactor of varying sizes, in which the temperature of the reaction material and all related key process parameters are accurately monitored, and real-time data can be obtained with accurate results.

[0009] The method for obtaining reaction kinetic parameters using online reaction calorimetry technology of the present invention comprises the following steps:

[0010] Step 1: By designing an experiment, a real-time heat release rate curve at a certain reaction temperature is obtained, and then a real-time thermal conversion curve is obtained. Finally, simple calculation and fitting are performed to obtain the reaction order and rate constant at the reaction temperature;

[0011] Step 2: Then, by designing a series of experiments at different reaction temperatures, the rate constant at the corresponding temperature is obtained by the method of step 1, and the activation energy and pre-exponential factor can be obtained by simple calculation and fitting. This method is simple and convenient, and does not require the use of professional chemical software for complex calculations.

[0012] Assume that the main reaction equation is as follows:

[0013] A+B→C+D+Δ r H

[0014] In the formula,

[0015] A, B: reactants;

[0016] C, D: products;

[0017] Δ r H: reaction exothermic enthalpy, unit: J.

[0018] Generally, when the above main reaction is an intermittent reaction with a selectivity of not less than 90% (preferably not less than 95%), a volume change before and after the reaction of less than 10% (preferably less than 5%), and no physical thermal effects such as crystallization and gas overflow, it can be considered that the Δ r H is the exothermic enthalpy of the main reaction, and the reaction rate of reactant A is -r A is the main reaction rate, then:

[0019]

[0020] In the formula,

[0021] -r A : Reaction rate based on reactant A, unit mol / L / s;

[0022] q: reaction exothermic rate, unit: W or J / s;

[0023] Δ r H m，A : The molar exothermic enthalpy of the reaction based on reactant A, in J / mol;

[0024] V: reaction volume, unit: L.

[0025] When B is in large excess (usually greater than 5 times its theoretical reaction amount, preferably greater than 10 times its theoretical reaction amount), the reactant A can be considered to be completely converted when the reaction stops releasing heat. At this time, the conversion rate of reactant A is approximately equal to the thermal conversion rate. Due to the large excess of reactant B, the concentration of reactant B changes very little (C B ≈C B，0), the effect of the concentration change of reactant B on the main reaction rate can be ignored. It is approximately assumed that the main reaction rate has nothing to do with the concentration of reactant B and only depends on the concentration of reactant A in the system. The main reaction rate equation can be expressed as:

[0026]

[0027] After substituting formula 1-1 into formula 1-2, the expression is:

[0028]

[0029] lnq=n×lnC A +ln[k′×Δ r H m，A ×V]

[0030] lnq=n×ln[C A，o ×(1-X)]+ln[k′×Δ r H m，A ×V] 1-3

[0031] In the formula,

[0032] q: reaction exothermic rate, unit: W or J / s;

[0033] k′: Corrected rate constant, the unit is related to the reaction order;

[0034] C A，0 : initial concentration of reactant A, mol / L;

[0035] C A : Real-time concentration of reactant A, mol / L;

[0036] n: reaction order of reactant A, dimensionless;

[0037] Δ r H m，A : The molar exothermic enthalpy of the reaction based on reactant A, in J / mol;

[0038] X: thermal conversion rate, dimensionless;

[0039] V: reaction volume, unit: L.

[0040] According to the real-time heat release rate curve and real-time thermal conversion rate curve of step 1 above, q, Δ r H m，A and X values, according to the above formula 1-3, lnq changes with ln[C A，o The slope of the fitting curve is the reaction order n of reactant A, and the corrected rate constant k′ can be obtained from the intercept of the fitting curve.

[0041] In step 2, when the reaction is carried out at different temperatures (the temperature interval is usually 5-20°C, and the preferred condition is 5-10°C), the modified rate constant k' at different temperatures can be obtained according to the above method. According to the Arrhenius formula:

[0042]

[0043]

[0044] In the formula,

[0045] k′: Corrected rate constant, the unit is related to the reaction order;

[0046] A′: corrected pre-exponential factor, the unit is the same as k;

[0047] E a : activation energy, unit J / mol;

[0048] R: ideal gas constant, 8.314, unit: Pa·m 3 / mol / K;

[0049] T: reaction temperature, unit K.

[0050] After obtaining the modified rate constant k' at different temperatures, a linear fit is made to the variation trend of lnk' with 1 / T according to formula 1-4. The activation energy E can be obtained from the slope and intercept of the fitting curve. a , the corrected pre-exponential factor A′.

[0051] In a specific embodiment of the present invention, a preferred method for obtaining reaction kinetic parameters using online reaction calorimetry is provided, comprising the following steps:

[0052] (1) Assume the reaction equation is A+B→C+D+Δ r H, reactant B is in large excess, the material is added to the reaction calorimeter, the reaction conditions are adjusted, and a real-time heat release rate curve at a certain reaction temperature is obtained;

[0053] (2) integrating the real-time heat release rate curve obtained in step (1) to obtain the reaction exothermic enthalpy, calculating the molar reaction exothermic enthalpy based on reactant A from the reaction exothermic enthalpy, normalizing the reaction exothermic enthalpy to obtain the real-time heat conversion rate curve;

[0054] (3) According to the above formula 1-3, lnq follows ln[C A,o ×(1-X)], the slope of the fitting curve is the reaction order n of reactant A, and the corrected rate constant k′ is obtained from the intercept of the fitting curve;

[0055] (4) designing a series of experiments with different reaction temperatures and other conditions consistent with step (1), and obtaining the corrected rate constant k′ at different temperatures according to the methods of steps (2) and (3);

[0056] (5) According to the above formulas 1-4, lnk′ The changing trend of is linearly fitted, and the activation energy E is obtained from the slope and intercept of the fitting curve. a , the corrected pre-exponential factor A′.

[0057] The present invention has the following beneficial effects:

[0058] 1. The various reaction parameters used in the present invention can be detected in real time by an online reaction calorimeter, which is simple and convenient to operate, and the results are accurate and reliable, and more in line with the actual situation.

[0059] 2. The present invention selects parameters such as exothermic reaction rate and reaction exothermic enthalpy to calculate reaction kinetic parameters. These parameters can be detected in real time by a reaction calorimeter. The reaction kinetic parameters obtained by simple calculation and fitting are highly accurate and do not require professional chemical software for complex calculations.

[0060] 3. The method of the present invention overcomes the problem that the equal time interval sampling method cannot accurately obtain the process of rapid change of reactant concentration and the equal conversion rate interval sampling method cannot accurately detect the reactant concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is the RC1 test curve (20°C) of the acetic anhydride alcoholysis reaction of Example 1.

[0062] Figure 2 The alcoholysis reaction of acetic anhydride in Example 1 is lnq with ln[C A，o ×(1-X)] changing trend fitting curve.

[0063] Figure 3 This is the fitting curve of the variation trend of lnk′ of the acetic anhydride alcoholysis reaction with 1 / T in Example 1. DETAILED DESCRIPTION

[0064] The present invention is further explained and illustrated by specific examples below. The following examples are only illustrative and do not limit the contents thereof.

[0065] Unless otherwise specified, the following concentrations are all mass percentages.

[0066] Example 1

[0067] In this example, a reaction calorimeter RC1 was used to study and obtain the kinetic parameters of the alcoholysis of acetic anhydride: reaction order, activation energy and pre-exponential factor, and the steps were as follows:

[0068] Acetic anhydride alcoholysis reaction equation:

[0069]

[0070] Brief description of the experimental process:

[0071] 150 g of 99.7% ethanol (molar mass 3.2 mol, density 0.79 g / mL) was added at one time, stirring was started, the temperature in the reactor was set (a total of 5 experiments were carried out, and the temperatures in the reactor were 5°C, 10°C, 15°C, 20°C, and 25°C, respectively). After each curve was stable, the program of the reaction calorimeter was selected for rapid calibration. After the calibration, 33 g of 98.5% acetic anhydride (molar mass 0.32 mol, density 1.08 g / mL) was added at one time. After each curve was stable, 1.6 g of 98% concentrated sulfuric acid (density 1.84 g / mL) was added dropwise. After the reaction was no longer exothermic, rapid calibration was performed and the experiment was terminated.

[0072] The RC1 test curves obtained at different temperatures were obtained, the heat release rate curves in the RC1 test curves were integrated to obtain the reaction exothermic enthalpy, and the reaction exothermic enthalpy was normalized by software processing to obtain the thermal conversion rate curve. Among them, the RC1 test curve obtained when the kettle temperature was 20°C is as follows: Figure 1 As shown, Figure 1 The RC1 test curve is shown in Table 1.

[0073] Table 1: Figure 1 RC1 test curve legend

[0074]

[0075] The heat release rate curve in the RC1 test curve obtained when the temperature in the kettle was 20°C was integrated to obtain a reaction exothermic enthalpy of 17.928 kJ. According to the reaction conditions, Δ r H m,醋酸酐 , V and C 醋酸酐，0 ,as follows:

[0076] Δ r H m,醋酸酐 =17.928kJ / 0.32mol*1000=56025J / mol.

[0077] V=33g / 1.08g / mL+150g / 0.79g / mL+1.6g / 1.84g / mL=221.3mL=0.2213L.

[0078] C 醋酸酐，0 =0.32mol / 0.2213L=1.446mol / L.

[0079] According to formula 1-3, for lnq with ln[C A,o ×(1―X)] to make a linear fit (see Figure 2 ), goodness of fit R 2 ≈0.99937, the fitting effect is good. The slope of the fitting curve gives the reaction order of acetic anhydride n = 1.01, and the corrected rate constant k′ = e∧3.20 / 56025 / 0.2213 = 0.00198s -1 According to the same method, the reaction order n and the corrected rate constant k' of acetic anhydride at reaction temperatures of 5°C, 10°C, 15°C and 25°C were calculated respectively, as shown in Table 2. As can be seen from Table 2, the average reaction order of acetic anhydride is 1.09, which is approximately 1st order.

[0080] Table 2: Acetic anhydride reaction order n and corrected rate constant k′ at different reaction temperatures

[0081] Reaction temperature / ℃ n <![CDATA[k′ / s -1 ]]> 5 1.18 0.000414 10 1.10 0.000687 15 1.05 0.00110 20 1.01 0.00198 25 1.10 0.00217

[0082] According to formula 1-4, a linear fit is made for the variation trend of ln k' with 1 / T (see Figure 3 ), goodness of fit R 2 =0.96334, the fitting effect is good. The activation energy Ea is obtained from the slope of the fitting curve = 7260.98*8.314 / 1000 = 60.37 kJ / mol, and the corrected pre-exponential factor A' = e∧18.36 = 94112365s -1 .

Claims

1. A method for obtaining reaction kinetic parameters using online reaction calorimetry, characterized in that The following steps are involved: (1) Assume the reaction equation is A+B→C+D+Δ r H, reactant B is in large excess; the materials are added to the reaction calorimeter, the reaction conditions are adjusted, and a real-time heat release rate curve at a certain reaction temperature is obtained; (2) integrating the real-time heat release rate curve obtained in step (1) to obtain the reaction exothermic enthalpy, calculating the molar reaction exothermic enthalpy based on reactant A from the reaction exothermic enthalpy, normalizing the reaction exothermic enthalpy to obtain the real-time heat conversion rate curve; (3) According to formula 1-3, lnq follows ln[C A，o ×(1-X)], the slope of the fitting curve is the reaction order n of reactant A, and the corrected rate constant k′ is obtained from the intercept of the fitting curve; lnq=n×ln[C A，o ×(1-X)]+ln[k′×Δ r H m，A ×V] 1-3 In the formula, q: reaction exothermic rate, unit: W or J / s; k': Corrected rate constant, the unit is related to the reaction order; C A,0 : initial concentration of reactant A, mol / L; n: reaction order of reactant A, dimensionless; Δ r H m，A : The molar exothermic enthalpy of the reaction based on reactant A, in J / mol; X: thermal conversion rate, dimensionless; V: reaction volume, unit L; (4) designing a series of experiments with different reaction temperatures and other conditions consistent with step (1), and obtaining the corrected rate constant k′ at different temperatures according to the methods of steps (2) and (3); (5) According to formula 1-4, lnk′ The changing trend of is linearly fitted, and the activation energy E is obtained from the slope and intercept of the fitting curve. a , the corrected pre-exponential factor A′; In the formula, k′: Corrected rate constant, the unit is related to the reaction order; A′: corrected pre-exponential factor, the unit is the same as k; E a : activation energy, unit J / mol; R: ideal gas constant, 8.314, unit: Pa·m 3 / mol / K; T: reaction temperature, unit K.

2. The method according to claim 1, characterized in that: In step (1), the main reaction shown in the reaction formula is an intermittent reaction with a selectivity of not less than 90%, a volume change before and after the reaction of less than 10%, and no crystallization and no gas overflow.

3. The method according to claim 2, characterized in that: In step (1), the main reaction shown in the reaction formula is an intermittent reaction with a selectivity of not less than 95%, a volume change before and after the reaction of less than 5%, and no crystallization and no gas overflow.

4. The method according to claim 1, characterized in that: In step (1), the amount of reactant B added is not less than 5 times its theoretical reaction amount.

5. The method according to claim 4, characterized in that: In step (1), the amount of reactant B added is not less than 10 times its theoretical reaction amount.

6. The method according to claim 1, characterized in that: In step (4), in a series of experiments designed, the interval between adjacent reaction temperatures is 5-20°C.

7. The method according to claim 6, characterized in that: In step (4), in a series of experiments designed, the interval between adjacent reaction temperatures is 5-10°C.

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